Baxi Solo HE Incorrect Combustion

I fitted a brand new Baxi Solo 18HE today, and when I went to commission it the combustion was not correct. The CO level was around the 200ppm mark, so I left it to run for a while hoping that it may just be burning off some of the oils from production but this did not solve the problem. Rechecking the combustion the CO2 was at 10.3% which is higher than it should be. I checked the gas rate and the meter was passing one cubic foot in approximately 45 seconds, which when referring to the tables is an input of 24kW. The working pressure was 20 Mbar at the meter and 18.5 Mbar at the boiler inlet.

I spoke to Baxi's technical department who suggested it may be something to do with the plugs on the PCB and asked me to check them. On the second plug from the bottom, there are two links, the colours and number of which depend on the boiler output. The links are actually resistors which alter the fan speed settings according to the boiler output. The links on the 18kW model are yellow and grey. They also suggested it was caused by the difference in gas pressure over the pipework or that the flue may not have been incorrectly assembled. All valid suggestions but not in this case. We tried another PCB, but that made no difference.

The solution was to replace the gas valve with a new one. This gave us CO of 40ppm, and CO2 of 8.5% which is within the manufacturers tolerance of 9% +/-1%. Not what you want when fitting a brand new boiler on a Friday.

Disclaimer: The works described in this blog are a record of work undertaken and should not be taken as guaranteed to solve your problem. Work should only be carried out by persons qualified and competent to do so.